By Cassandra Balentine
Like traditional two-dimensional (2D) printers, printheads drive three dimensional (3D) printing technology. There are many additive manufacturing techniques for achieving a 3D printed object. The International Organization for Standardization (ISO/ASTM 52900:2015) offers seven broad categories for additive manufacturing technologies—binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and vat photopolymerization. Within these categories, select methods utilize printhead technology.
Several printhead manufacturers in the 2D print space have ventured into the 3D market. This transition brings subtle printhead differences along with benefits and challenges.
Above: Examples of output from a 3D printer equipped with Xaar printheads.
From a printhead standpoint, the technology driving 3D printers is essentially the same as what is found in 2D technology. At a basic level, both 2D and 3D printheads print an image one page, layer, or slice at a time. With 3D printing, layers are stacked on top of each other to create the object.
Rather than depositing the ink on a moving piece of paper, Gavin Zau, SVP, Asia Pacific, Memjet, points out that with 3D printing the printing mechanism scans over the print bed to deposit the materials or the binder to glue the material together in order to create a 3D object.
Piezoelectric drop on demand printheads from the 2D print space are taken from the graphics, ceramics, and desktop printing markets and utilized in 3D machines for a quick solution that does not require changes to the printhead architecture. “These machines are limited in their capability and are fluid specific,” explains Simon Kirk, senior product manager, Xaar.
He sees an increasing number of 2D printheads being adapted for 3D machines and/or the OEM. “No piezoelectric inkjet 3D printhead has been designed from the ground up, but instead 2D inkjet printheads—which are designed to meet the needs of industrial and commercial print applications and their typical fluids—are modified to cope with the 3D fluids and materials,” states Kirk.
He says there are 2D printheads with some modification made to them so they are bespoke to an OEM, their fluids, and applications. “So far, very little 3D piezoelectric inkjet printhead design has been carried out; it has been mostly an adaptation of current 2D printheads for specific fluid types,” continues Kirk.
Dr. Tristan Downing, Dr. Chris Hole, and Dr. Richard J. Tweedie, consultants, TTP plc, agree, adding that, “currently, within true 3D printing, most products use 2D printheads either unmodified or only slightly modified.”
Memjet’s printheads, for example, use the same page width printing technology for both 2D and 3D printing processes. In 3D binder jetting, instead of paper moving underneath the printheads, the printhead scans over a bed of powder, laying down the binder to build one layer of the 3D object. By repeating the process of laying down a layer or powder and page wide binder printing, the 3D object is built up.
The benefits of this process are similar for 2D and 3D printing. Zau says Memjet’s hardware provides high-speed 3D printing capabilities, so the 3D print provider wins with a less risky investment and more productive solution. He adds that higher print speeds also equate to better service with faster turnarounds.
HP Inc. also leverages its 2D technology for 3D. The company utilizes its expertise in thermal inkjet and builds on its PageWide technology. “Our thermal inkjet technology gives us an advantage and is what we call our ‘Inkjet Moore’s Law.’ We are all familiar with Moore’s Law, where the number of transistors on a microchip doubles every 18 months. Starting over 30 years ago, we have doubled the number of drops our printheads can deliver every 18 months. What started as 18,000 drops per second in 1984 is now into the hundreds of millions of drops per second, with high degrees of precision, and continuing to grow exponentially. Our 3D printing solutions leverage this technology to deliver the agents, binders, and voxel-level—21 micros across, to enable 3D plastic and metal manufacturing,” explains Cheryl Macleod, global head of 3D science and materials expansion, HP. Taking advantage of the company’s legacy of printhead innovation, HP designs 3D printheads using virtually the same process as its 2D web presses and large format industrial printers. The 3D printheads are then customized to meet the unique needs of its agents.
For Fused Deposition Modeling (FDM) by applying release agent and adding color, there isn’t much difference between 2D and 3D printheads, except 3D requires higher temperature operation, comments John Harman, director sales and strategy, Ricoh Printing Systems of America, Inc. He also suggests that for powder bed technology, there isn’t much difference between 2D and 3D printheads, except 3D requires larger drop volumes.
3D Printhead Design
Printheads are specific to the printing method employed. For example, FDM extrusion printheads are different compared to binder fluid printheads or photopolymer printheads, offers Kirk.
Downing, Hole, and Tweedie note that while the analogy of 3D printheads works well for 3D methods like direct jetting technology, the majority of metal additive manufacturing applications are based on powder bed fusion—either direct sintering or binder jetting. “Therefore, the printhead only forms a small part of the science behind the systems. The speed of processing, required tolerance, surface finish, and material of the part affect the decision as to which of the print technologies would be better suited to the application.”
The construction of the printhead is dependent on the physical and chemical properties of the material ejected. “Surface tension, viscosity, and chemical compatibility are key factors in determining which off-the-shelf printhead to use, or whether further printhead development is required,” they explain.
There is a clear opportunity in the 3D market to offer a printhead that can jet a range of viscosities at different temperatures with good material compatibility and protection from interference with printhead functions, which enables OEMs to provide different machines from different applications, and also allow them to provide clear benefits in cost and scaling, according to Kirk.
The design of piezoelectric inkjet 3D printheads must take into account a wider range of viscosities to jet a variety of materials. “This gives OEMs the ability to offer a range of part properties or functionalities,” says Kirk.
Another critical consideration of 3D printhead design is fluid compatibility. “While an FDM printhead can be made of stainless steel or other inert materials with coatings to protect it, the choice of specification, flexibility, and conductivity of materials to be used in a piezoelectric printhead is much narrower. Designers must ensure the fluid doesn’t interface with the operation of the actuation of the PZT as well as prevent conductivity, corrosive interaction, and sedimentation or fluid separation. It’s a tricky business designing a 3D piezoelectric printhead,” admits Kirk.
Downing, Hole, and Tweedie point out next-generation products using printheads specifically designed for 3D use key requirement differences, like the ability to eject different materials—most 2D printer inks are either water- or UV-curable polymer based. 3D printing tends to focus on structural polymers like ABS or materials with solid particles from them; higher material flow rates—2D printers typically use small amounts of ink in comparison so 3D printheads must shift more fluid to keep fabrication times down; longer printhead lives; more homogeneous drip sizes; the ability to fire adjacent nozzles continuously and simultaneously; and high temperature operation.
Filaments are used in FDM 3D printers. The most common FDM printers are found in consumer applications and print with plastic filaments, states Zau. However, more advanced commercial FDM printers offer filament for metal, high temperature plastics, and ceramics. “Some systems have high precision printheads and mechanisms for high-resolution printing while others have multiple printheads to increase throughput,” he comments.
As a newer technology, the road to 3D printing adoption is paved with many challenges. These include performance considerations, scaling for production, and finding the right chemistry and print technology for the project at hand.
The printhead’s performance to facilitate long build times, the ability to use a wide array of fluid and materials, and delivering desired and increasingly higher flux rates are part of this, says Harman.
Downing, Hole, and Tweedie suggest the primary challenges in working with 3D printers—especially as the technology moves from prototype to full-scale production—is the qualification of materials and processes for new applications and products. Post processing is also an issue, which is more labor intensive and less amendable to automation at this time.
Macleod says modifying printheads for 3D printing to meet the stringent demands of a more industrial landscape is a challenge. “For example, in 2D printhead development, you can look right over the machine. But in 3D printing when you spray ink on powder you need a sealed interface. This means that the environment starts to look more like a factory floor than a research and development lab.”
For all printing, managing dust and maintaining system cleanliness is a big concern, comments Zau. He adds that managing the powder and printhead maintenance are key concerns with binder jet 3D printing.
Kirk says the main challenge of working with 3D is the inherent inflexibility of the machines. “By this I mean the design of the 3D printer that prevents settings from being adjusted, fluids from being tailored to the parts, and parts generation from being tailored to the environment or other characteristics. By making the printer limited in its function and flexibility, the industry has limited the expansion of 3D in production-level volumes and adoption. A printer that can only produce specific parts or tolerances and properties with certain materials is limiting to those looking to expand material offerings to their customers and those looking to innovate or consolidate existing parts.”
Responding to Growth
The growth of 3D printing requires new solutions across all points of the supply chain, including the production of materials and the characterization and qualification of materials, processes, and parts, offer Downing, Hole, and Tweedie.
HP’s Multi Jet Fusion technology is built on core HP intellectual property. In conjunction with HP partners in its open ecosystem, the company works to transform the value chain by improving the capabilities of its Multi Jet Fusion products, lowering the cost of 3D printing materials in the plastics space, driving a greater amount of variety of 3D printing materials, developing new design methods for additive manufacturing, reinventing supply chains, and working within the industry and governments to establish a set of regulations and standards.
Memjet page wide printing technology offers a higher print speed compared with traditional scanning, smaller printhead printers, says Zau. He explains that this level of productivity enables faster turnaround for 3D print providers and helps to deliver better customer service and higher profitability.
Ricoh is a developer and manufacturer of printheads for the 3D print market. It has worked closely for over 20 years with many printer OEMs to understand and deliver the printhead performance requirements necessary to drive the success of the 3D print market. For direct material jetting, Ricoh’s 3D printheads are designed to deliver larger drop volumes between 15 to 80 picoliters, handle higher temperatures, and support fluid re-circulation or flow through printhead functionality.
TTP has developed print technologies for 30 years. Its current expertise extends from development of printhead technology to the formulation of powders. “3D printing methods that use printheads form a significant part of the overall additive manufacturing market, since it is a critical element in more than one technique. Future printheads will need to cope with broader uses as increased accuracy and speed drives use of printheads over traditional methods of deposition,” say Downing, Hole, and Tweedie.
Xaar supplies 3D printer OEMs with printheads that enable them to jet a range of viscosities at an array of temperatures with good compatibility and protection from interaction. Xaar piezoelectric inkjet printheads are not specific for material types and can be used to jet binders, photopolymers, highly viscous fluids, and conductive inks. “As long as the fluid is within the printheads viscosity range at jetting temperature and it has compatibility with the fluid path materials, then essentially you’re good to go,” says Kirk.
2D printhead manufacturers are adapting to a new dimension. Evolution continues as 3D printing technologies are enhanced.
Feb2019, Industrial Print Magazine